Colorectal cancer is the second most common cause of cancer deaths in the US. A better understanding Of its pathOgenesis might lead to earlier diagnosis and/or prevention of this disease. Aberrant crypt foci (ACF) are the earliest identified putative precursors of colon cancer. They are identified microscopically in whole-mount specimens of colon. ACF are seen (a) in rodents as early as 2 weeks after a single dose of carcinogen and (b) in humans at increased frequency in patients with colon cancer. ACF are by definition grossly invisible but resemble some lesions identified at endoscopy and may include some small "flat adenomas." The overall aim of these studies is to test the hypothesis that ACF are putative preneoplastic lesions in human colonic mucosa and that subpopulations of these lesions progress to colon cancer. The following studies will be carried out to test this hypothesis, i.e., that at least some ACF are neoplastic and not merely hyperplastic lesions. The expression of phenotypic markers thought to be related to neoplasia will be compared in histological sections of human ACF and "flat adenomas." The phenotypic alterations to be examined as candidate markers for premalignant or malignant colonic epithelium include (a) the presence and degree of dysplasia, (b) carcinoembryonic antigen (CEA), (c) the adhesion molecule CD44, (d) mucin antigens, and (e) products of the suppressor genes APC and p53. Genetic alterations that are thought to occur early in the pathogenesis of colon cancer such as mutations in APC and K-ras genes and genomic instability will be determined in a larger number of ACF from patients with sporadic colon cancer with PCR-amplified DNA from microdissected tissue. When ACF have 15 or more crypts, a portion of the ACF will be embedded for the evaluation of dysplasia in longitudinal sections and the remaining portion will be microdissected for DNA amplification. ACF from patients (a) with sporadic colon cancer, (b) with familial polyposis, and (c) without colon cancer will be analyzed for clonality with X-linked chromosomal markers and molecular techniques after PCR. Chromosomal abnormalities detected with in situ DNA probes will be compared in ACF and "flat adenomas." Specific characteristics of ACF and "flat adenomas" in the whole-mount specimens will be correlated with the above findings and/or with dysplasia observed in these lesions.